Propeller



June 6, 1939.

G. R. M ERTENS PROPELLER Filed Dec. 1, 1936 ORNW 5 m 6 m mwnm MW mb 0 GY. B

AL! 1 ATT Patented June 6, 1939 UNITED STATES PATENT oFFicE PROPELLERGabriel K. Mertens, Darby, Pa. Application December 1, 1936, Serial No.113,547

1 Claim.

My invention relates to a screw propeller adapted for use on powerpropelled boats. The invention consists in a continuous screw propellerhaving a graduated pitch of its blades from the 5 front towards the rearof the boat or vessel and having a blade which decreases in diameterfrom the front to the rear part of the blade.

I-Ieretofore vessels have experienced considerable vibration from theuse of a screw type of propeller. This vibration is brought about by theunbalanced propeller, for one reason; and second, the churning of waterfrom one side to the other.

By my invention I have been able to eliminate l5 vibration and increasethe speed of the boat for the same power input. As a corollary bydecreasing the power, I have been able to secure the same speed in aboat of the same size under like conditions where my new and improved goscrew propeller is used.

Objects of my invention are to provide a screw propeller which inproportion to its size is possessed of large capacity. The propellerwill not be damaged or broken by engaging objects in the 5 water, andthe propeller will take firm hold of the water at all times andconsequently will not subject the driving engines to sudden shocks andstrains.

My invention comprises a continuous screw which (first) decreases fromfront to rear in a direct geometric ratio, and (second) this continuousscrew blade decreases in diameter from the front to the rear so as tooutline a truncated cone, as will be further explained in detail, and(third) the blade in crosssection is concave on one side and convex onthe other side.

It also should be noted that my new propeller does not require a greatdepth of immersion so that a vessel equipped with my improved propellercan move in comparatively shallow Waters.

Further, where the ordinary propeller blade might be raised out of thewater due to the pitching and the tossing of the vessel and then comedown with a sharp blow, this would not occur with my propeller,particularly since the blade is properly balanced.

My invention provides little or no vibration to the shaft and has aslight tendency to throw waves on eitherside of the course of thevessel.

It is also to be observed that the structure of the blade eliminatesdanger of the blade being broken by contact with logs or other solidobjects which infest the waters. The uniform action of 55, the worm typeof propeller against the water diconvolution minishes the jarring of theengines and vibration in ships, which vibration is at presentobjectionable. This vibration is in a large measure caused by the lackof a continuous form of action of the propellers against the water.

With the above and related objects in view, my invention consists in thefollowing details of construction and combination of parts, as will bemore fully understood from the following description, when read inconjunction with the accompanying drawing, in which:

Fig. 1 is a side elevational view of my invention as applied to avessel.

Fig. 2 is a view from the line 2-2 of Fig. 1.

Fig. 3 is a schematic side elevational view of the relative position ofthe convolutions of the propeller.

Fig. 4 is a sectional view of the upper portion of the front convolutiontaken on the line 4-4 of Fig. 2.

Referring now in greater detail to the drawing, I show my inventionembodied on a boat, vessel, or ship, generally designated as A. Myinvention is mounted upon a rotatable shaft H], which is suitablymounted on a bearing, or bearings. The shaft is suitably connected to asource of power (not shown) whereby the shaft is rotated.

My improved propeller, of the continuous screw type and of a spiralconstruction, is composed of a plurality of convolutions I2, [4, l6, i8,20 and 22 receding in appropriate proportions from the front to the backand decreasing in diameter outwardly from the front to the back. Thefirst [2 of a maximum diameter, designated as L is nearest the source ofpower, and as the convolution moves a distance D through 360, thediameter of the helix or convolution decreases. A second helix 14 ofmaximum diameter is a continuation of the helix I2 and is a definitegeometric proportion smaller than the first helix I2, and the helix I4makes one complete turn for a distance designated as D see Fig. 3.

At this point, it is to be observed and carefully noted that thedistance D through which the helix l4 passes, is less than the distanceD through which the helix I2 passes. This is illustrateddiagrammatically in Fig. 3.

The ratio of taper is that the angle X of the cone shown in Fig. 3 is anangle whose tangent is A,. In other words, the outer edge ofconvolutions must be in the curved surface of the outline of a truncatedcone whose generatrix and medial axis defines an angle whose tangent isThe helix [6 is of less diameter than the aforementioned helixes l2 andI l, and the distance, designated as D, along the axis of the shafttraversed by the helix [6 is in proportion to its maximum diameter D Thehelixes I8, 26 and 22 are constructed in the same pitch ratio anddiametrical ratio as the previously mentioned helixes l2, l4 and I6.

Six convolutions of the propeller preferably are used, and they coverfive-eighths of the medial axis of the outline of the theoreticaltruncated cone, and the diameter of the base of the truncated cone isone-half the height of the full cone. In other words, if the base is 20inches, the height of the cone is 40 inches, and the convolutions of theblades will extend for 25 inches.

A schematic diagram shown in Fig. 3 illustrates that the decrease indiameter of each helix is directly proportioned to the distance thehelix travels as measured along the axis of the shaft. Hence, since theratio of diameter is a direct proportion of the length as measured alongthe axis, the tip of each blade will lie in the same straight line.

Expressed in another manner, the contour or outline produced by therevolution of the propeller is a truncated cone. The longitudinaldistance decreases along the shaft from one convolution of the blade tothe next convolution.

In other words, the pitch, which is the amount of advance of ascrew-thread in a single turn, decreases from front to rear for eachconvolution. This decrease in pitch is in accordance with the definitearithmetical ratio aforementioned.

F'or the sake of emphasis as to the efficiency produced with myinvention, I shall assume for the purposes of illustration that thevessel is stationary while its propeller is revolved. Considering theforward convolution l2 and the water acted upon by that convolution, therevolving of the convolution would be to drive the body of waterrearwardly in a straight line extending diagonally away from the axis ofthe propeller; this is the resultant effect of the centrifugal force ofthe revolving inclined or camlike surface of the blade. This movement islikewise theoretically true of each separate body of water acted upon byeach separate part of the blade. The convolution also gradually releasesdead water or water which is not effective.

Hence, if the vessel be stationary, the water is forced rearwardly by ascrew in a series of frustoconical sheets-the apex of each being in theaxis of the propeller shaft and the cone base extending rearwardly; andsome dead water is also forced rearwardly through each convolution.

It is to be observed that there would be no effect on the water reachingthe next succeeding convolution since the next succeeding convolution isof a smaller diameter, so that the particular body of water being drivenback by its predecessor blade does not interfere with that particularbody of water. However, each blade is sufiiciently far out radially asto act upon a fresh portion or portions of water which have not beenbroken up by the precedent portions of the blade, and the blade orconvolution also acts on a part of the dead water. Under suchcircumstances, a maximum driving effect is obtained.

In the above discussion, the assumption was made that the vessel wasremaining stationary while the propeller was revolving, but theprinciple is equally the same if the vessel is considered as being inmotion. The successive bodies of water are passing simultaneously andconstantly from every successive portion of the blade (withoutinterference from any other part of the blade) while the vessel and thepropeller are themselves likewise advancing forwardly.

Further, since the vessel is going ahead, the rearward parts of theblade are constantly being brought into position where they are actingupon waters which may already be broken up by the forward portions ofthe blade and which ordinarily'cause a suction or drag on the blade.

There is no requirement for placing the propeller blade in a taperingtunnel.

I prefer to form the entire worm propeller in one integral casting, asis shown in the drawing, but the worm may, of course, be formed inseparate sections securely united together. The worm propeller outsidefrom its other improved advantages is of an outline presenting greatstrength and durability.

Although my invention has been described in considerable detaiL suchdescription is intended as illustrative rather than limiting, since theinvention may be variously embodied, and the scope of the invention isclaimed.

I claim as my invention:

An integral boat screw propeller comprising a central shaft, acontinuous blade comprising a plurality of complete convolutionssurrounding said shaft, said convolutions decreasing in pitch from thefront to the rear in a direct arithmetical progression, the diameter ofeach convolution of the propeller decreasing in diameter l.

by a direct arithmetical progression from the front to the rear, theconvolutions arranged to have their edges within the outline of a conewhose pitch extends for -.a distance of fiveeighths of the length of themedial axis of said cone, and the outline of a truncated cone whosemedial axis forms an angle with the generatrix of the truncated cone sothat the tangent of the angle is approximately 0.25.

GABRIEL R. MERTENS.

